The present invention relates to powder homogenizing apparatus, to its use and to a homogenizing method using said apparatus.
More specifically, but not exclusively, the present invention relates to a powder homogenizing apparatus that is specially adapted to a heat-releasing noxious powder, in particular a radioactive powder such as plutonium oxide, more particularly plutonium dioxide (PuO2).
Such a homogenizing apparatus must simultaneously satisfy requirements as to homogeneity, grain size and isotopic composition of the powder, and avoid segregation, while also removing the heat released from the noxious powder per se and produced by agitating it.
A further aim of the present invention is to provide a homogenizing apparatus for a noxious powder that can be integrated into a treatment line between upstream and downstream apparatus, which can also evacuate the powder towards downstream apparatus while monitoring and regulating the flow rate of the powder from the homogenizing apparatus to the downstream apparatus.
Powder homogenizing apparatuses that have been proposed up to the present time cannot effectively satisfy all of those conditions.
The present invention satisfies those conditions by providing powder homogenizing apparatus comprising:
a cylindrical shell of circular section and of substantially horizontal axis, which shell is sealed and with a cylindrical barrel closed at its ends by two disk-shaped end plates, said shell being provided with at least one filler orifice located in the upper portion of said shell and at least one discharge orifice opening into the bottom of said shell;
an assembly of cylindrical drums of circular section located inside the shell with which it is coaxial and fluidtight, said drum assembly comprising an inner drum and an outer drum each provided with a cylindrical wall closed at its ends by two disk-shaped walls, the external face of the cylindrical wall of said outer drum being overlaid with blades capable of homogenizing the powder contained in the annular space formed between the cylindrical wall of the outer drum and the barrel of the shell, a space of revolution being formed between said inner and outer drums;
a shaft disposed along said longitudinal axis through said cylindrical shell, mounted on a bearing at each end plate and on which said assembly of cylindrical drums is mounted in integral manner, said shaft comprising a first end portion provided with a first internal longitudinal channel and a second end portion provided with a second internal longitudinal channel, said first channel being connected, outside the shell, to a system for supplying cold air and said first end portion being provided inside said shell with at least one supply orifice for providing cold air to said space of revolution from said first channel, said second end portion being provided, inside said shell, with at least one exhaust orifice placing said space of revolution in fluid communication with said second channel, and said second channel being connected, outside said shell, to an air exhaust system to release air from said space of revolution, a sealing system being provided for each bearing; and
drive means for rotating said shaft.
It should be understood that this solution uses an internal system for cooling the homogenizing apparatus and the powder it contains. It should also be understood that this solution enables homogenization to be carried out by mixing powder contained in the annular space formed between the cylindrical wall of the outer movable drum and the barrel of the fixed shell. The powder can be cooled by the presence of cold air inside the space of revolution defined between the outer drum and the inner drum, which results in a large heat exchange surface (the whole surface of the cylindrical wall of the outer drum) between the cold air and the powder.
The expression xe2x80x9caxial halfxe2x80x9d of the inner drum or the outer drum as used below will be used to mean one of the two portions (or first longitudinal half drum) of this drum separated from the other portion (or second longitudinal half drum) by a transverse plane that is orthogonal to the longitudinal or axial direction (X, Xxe2x80x2) of the drum, said transverse plane being located half way along the drum concerned. In FIGS. 1 and 2, this transverse plane is that containing axes (Y, Yxe2x80x2) and (Z, Zxe2x80x2).
Preferably, said blades are helical and form a screw pitch that is reversed with respect to the pitch of the other axial half of the outer drum.
Preferably again, the outer face of the cylindrical wall of each axial half of the outer drum is overlaid with an inner helical blade attached to said outer surface all the way along said axial half and with an outer helical blade spaced from said outer face along the entire length of said axial half, said inner and outer blades being of screw pitch that is reversed with respect to the pitch on the other axial half of the cylindrical wall.
To further improve heat exchange inside the homogenizing apparatus, the space defined between the outer drum and the inner drum is preferably provided with fins.
To improve the powder-cooling performance of the homogenizing apparatus, in a highly advantageous solution, at least the lower portion of said barrel is formed from a double-walled sealed jacket in which cold air from a cold air supply system can circulate.
Clearly, that disposition adds an external cooling system located outside the annular space containing the powder to the internal cooling system.
To improve the heat exchange capacities of said external cooling system, the face of the upper wall of said jacket facing the interior of said jacket is provided with fins.
The present invention also provides the use of a powder homogenizing apparatus of the type defined above, the apparatus being placed in a glovebox, said powder being radioactive and preferably constituted by plutonium dioxide (PuO2).
The present invention also provides a method of homogenizing and cooling a powder, using a powder homogenizing apparatus of the type defined above, the method comprising the following steps:
a) closing the discharge orifice;
b) activating said drive means to cause said shaft and said drum assembly to rotate;
c) activating said system for supplying cold air to fill and circulate cold air in the space defined between the outer drum and the inner drum;
d) opening said filler orifice to allow powder to enter said annular space between the outer drum and the barrel of the shell;
e) closing said filler orifice when the desired quantity of powder has been introduced into said annular space;
f) carrying out homogenization by rotating said shaft and said drum assembly; and
g) opening said discharge orifice to empty said annular space when homogenization is complete.